Book Image

Clojure High Performance Programming

By : Shantanu Kumar
Book Image

Clojure High Performance Programming

By: Shantanu Kumar

Overview of this book

<p>Clojure is a young, dynamic, functional programming language that runs on the Java Virtual Machine. It is built with performance, pragmatism, and simplicity in mind. Like most general purpose languages, Clojure’s features have different performance characteristics that one should know in order to write high performance code.<br /><br />Clojure High Performance Programming is a practical, to-the-point guide that shows you how to evaluate the performance implications of different Clojure abstractions, learn about their underpinnings, and apply the right approach for optimum performance in real-world programs.<br /><br />This book discusses the Clojure language in the light of performance factors that you can exploit in your own code.</p> <p>You will also learn about hardware and JVM internals that also impact Clojure’s performance. Key features include performance vocabulary, performance analysis, optimization techniques, and how to apply these to your programs. You will also find detailed information on Clojure's concurrency, state-management, and parallelization primitives.</p> <p>This book is your key to writing high performance Clojure code using the right abstraction, in the right place, using the right technique.</p>
Table of Contents (15 chapters)
Clojure High Performance Programming
Credits
About the Author
Acknowledgments
About the Reviewers
www.PacktPub.com
Preface
Index

Sequences and laziness


 

"A seq is like a logical cursor."

 
 --Rich Hickey

Sequences (commonly known as seqs) are a way to sequentially consume a succession of data. Like Java iterators, they let a user begin consuming elements from the head and proceed realizing one element after another. However, unlike Java iterators, sequences are immutable. Also, since sequences are only a view of the underlying data, they do not modify the storage structure of the data.

What makes sequences stand apart is they are not data structures per se; rather, they are a data abstraction over a stream of data. The data may be produced by an algorithm or a data source connected to an I/O operation. For example, the function resultset-seq accepts a JDBC java.sql.ResultSet instance as an argument and produces lazily-realized rows of data as a seq.

Clojure data structures can be turned into sequences using the seq function. For example, (seq [:a :b :c :d]) returns a sequence. Calling seq over an empty collection returns...